Search

In order to synthesize biochar with the enhanced adsorption of inorganic mercury (Hg(II)) and organic mercury (Methylmercury, MeHg), biochars pyrolyzed at different pyrolysis temperatures (300, 500, and 700 °C) were ball milled with 3-trimethoxysilylpropanethiol (3-MPTS). Characterization results showed that 3-MPTS acted as an activator which further enlarged pores in biochars and ball-milling increased surface area of biochars. During ball milling, oxygen-containing functional groups increased which facilitated the loading of -SH group. The maximum adsorption capacities for Hg(II) adsorption in ball mill sulfhydryl modified biochars of 300, 500, and 700 °C were 401.8, 379.6 and 270.6 mg/g, respectively; simultaneously, the maximum adsorption capacity of MeHg was 108.16, 85.27 and 39.14 mg/g, respectively, which showed preferential increasing of 5.54 times on MeHg compared to the non-thiol modified biochar at low pyrolysis temperature of 300 °C. Results of kinetic adsorption experiments suggested that sorption data fitted well with Pseudo-second-order kinetic model, which proved that the mainly rate-limiting adsorption step was surface diffusion. Langmuir isotherm model fitting result showed that ligand exchange, surface complexation, surface adsorption and electrostatic attraction are dominant removal mechanisms. The 3-MPTS content and ball milling time are crucial during ball milling, and 2% 3-MPTS and 30 h of ball milling were found to be the most suitable conditions for both Hg(II) and MeHg adsorption. The result suggests that ball milling aided thiol-modification has great potential in synthesis of -SH modified biochar with prioritized MeHg adsorption., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Modification of thiol on biochar often demands complex synthetic procedures and chemicals. In this work, a simple and environment friendly thiol-modified biochar (BMS-biochar) was successfully synthesized by ball milling pristine biochar with 3-mercaptopropyltrimethoxysilane (3-MPTS). The resultant BMS-biochar was characterized and tested for aqueous inorganic Hg 2+ and organic CH 3 Hg + removal. Characterization results showed that 3-MPTS was loaded on the surface of biochar through oxygen-containing functional groups (i.e., OH and CO) and π-π bond. Ball milling method improved the properties of BMS-biochar, namely, more efficient SH load, a larger surface area, more functional groups, more negatively charged surface, which resulted in higher removal efficiency of Hg 2+ and CH 3 Hg + (320.1 mg/g for Hg 2+ and 104.9 mg/g for CH 3 Hg + ) compared to the pristine biochar (105.7 mg/g for Hg 2+ and 8.21 mg/g for CH 3 Hg + ) and thiol-modified biochar through chemical impregnation (CIS-biochar) (175.6 mg/g for Hg 2+ and 58.0 mg/g for CH 3 Hg + ). Ball milling increased the sorption capacities of Hg 2+ and CH 3 Hg + through surface adsorption, electrostatic attraction, ligand exchange, and surface complexation. Modeling results suggested that the surface diffusion was the rate-limiting adsorption step for BMS-biochar. This work gave prominence to the potential of ball milling for the preparation of thiol-modified biochar to remove mercury especially organic CH 3 Hg + by adsorption., (Copyright © 2019 Elsevier B.V. All rights reserved.)

In this work, biochar (BC), activated carbon (AC), and graphene oxide (GO) were thiol-functionalized using 3-mercaptopropyltrimethoxysilane (3-MPTS) (named as BCS, ACS, and GOS, respectively). BCS, ACS, and GOS were synthesized mainly via the interaction between hydrolyzed 3-MPTS and surface oxygen-containing functional groups (e.g., -OH, O-C=O, and C=O) and π-π interaction. The materials before and after modification were characterized and tested for mercury removal, including sorption kinetics and isotherms, the effects of adsorbent dosage, initial pH, and ionic strength. Pseudo-second-order sorption kinetic model (R 2  = 0.992~1.000) and Langmuir sorption isotherm model (R 2  = 0.964~0.998) fitted well with the sorption data of mercury. GOS had the most -SH groups with the largest adsorption capacity for Hg 2+ and CH 3 Hg + (449.6 and 127.5 mg/g), followed by ACS (235.7 and 86.7 mg/g) and BCS (175.6 and 30.3 mg/g), which were much larger than GO (96.7 and 4.9 mg/g), AC (81.1 and 24.6 mg/g), and BC (95.6 and 9.4 mg/g). GOS and ACS showed stable mercury adsorption properties at a wide pH range (2~9) and ionic strength (0.01~0.1 mol/L). Mercury maybe removed by ligand exchange, surface complexation, and electrostatic attraction.

Graphical abstract Highlights • Low temperature (300 °C) pyrolyzed biochar was more suitable for thiol-modification. • Thiol-modification of biochar increased the adsorption of CH 3 Hg+ more obviously. • Hg2+ and CH 3 Hg+ were removed by surface complexation. • SH group played a major role during the uptake of Hg2+ and CH 3 Hg+. Abstract Biochars pyrolyzed at different temperatures were thiol-modified using 3-mercaptopropyltrimethoxysilane (3-MPTS) and applied on aqueous Hg2+ and CH 3 Hg+ removal with high efficiencies. The structure and physicochemical properties of biochar before and after thiol-modification were characterized. The biochar pyrolyzed at low temperature had more active sites (OH, C O, C O C, and π bond) for surface modification with 3-MPTS. Pseudo-second-order kinetic model and Langmuir isotherm model fitted well with the sorption data. Among all the raw and thiol-modified biochars, 3BS (thiol-modified biochar from pyrolysis at 300 °C) had the largest Langmuir adsorption capacities of Hg2+ (126.62 mg/g) and CH 3 Hg+ (60.76 mg/g). The introduction of SH enhanced the selectivity of biochar for mercury sorption (especially CH 3 Hg+). Ligand exchange and complexation between surface active sites (SH, OH, COOH, and NH 2) and mercury were the dominant removal mechanisms. Among them, SH played a major role. With the increase of 3-MPTS content in the preparation of 3BS, the adsorption capacity of Hg2+ and CH 3 Hg+ increased first and then decreased (the optimal content of 3-MPTS was 2%). Natural organic matter (NOM), glucose and humic acid (0–24 mg/L) had little effect on the adsorption of Hg2+ and CH 3 Hg+ by 3BS (the mercury removal rate only changed by 1.2–9.4%). This study demonstrates potential of thiol-modified biochar for mercury (especially CH 3 Hg+) removal from water. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • SGO/Fe-Mn effectively removes low concentrations of aqueous Hg2+ and CH 3 Hg+. • The maximum sorption capacity is 233.17 mg/g for Hg2+ and 36.69 mg/g for CH 3 Hg+. • Mercury were removed by ligand exchange and surface complexation. • SGO/Fe-Mn perform well at typical pH, IS, humic acid, and coexisting heavy metals. • SGO/Fe-Mn is applicable for mercury remediation in surface water and groundwater. Abstract A novel thiol-functionalized graphene oxide/Fe-Mn (SGO/Fe-Mn) was investigated for aqueous Hg2+ and CH 3 Hg+ removal. Mercury were removed mainly through ligand exchange and surface complexation with surface active sites (i.e., −SH, OH, O C O, C C, Si O, and π π bond). SH had the strongest binding ability with mercury, forming sulfur-containing organic matter or polymers with Hg2+, and sulfur-containing organometallic compounds or thiolate-like species with CH 3 Hg+. The BET sorption isotherm model well simulated the sorption isotherm data of Hg2+ (R2 =0.995, q m =233.17 mg/g) and CH 3 Hg+ (R2 =0.997, q m =36.69 mg/g), indicating a multilayer adsorption process. The mercury uptake was promoted with the increase of 3-MPTS content, adsorbent dosage, and pH (<5.5), whereas the uptake was inhibited by high pH (>5.5) and high concentrations of humic acid and electrolytes. SGO/Fe-Mn demonstrated high mercury uptake in simulated surface water/groundwater and in the presence of Pb, Cu, Ni, Sb, Cd and Zn. The mercury-laden SGO/Fe-Mn can be successfully regenerated and reused for three times with 98.1% and 67.0% of original Hg2+ and CH 3 Hg+ sorption capacity when 5% thiourea + 2 M KI was used as the desorbing agent. This study demonstrates potential and viability of SGO/Fe-Mn for mercury remediation. [ABSTRACT FROM AUTHOR]